Added tests on default arguments of fake overridden functions

compiler/testData/codegen/box/defaultArguments/implementedByFake2.kt

@@ -0,0 +1,42 @@
+// IGNORE_BACKEND: JVM, JS
+
+interface I<T> {
+    val prop: T
+
+    fun f(x: String = "1"): String
+
+    fun g(x: String = "2"): String
+
+    fun h(x: T = prop): T
+}
+
+interface I2<T> : I<T>
+
+open class A<T> {
+    open fun f(x: String) = x
+
+    open fun g(x: T) = x
+
+    open fun h(x: String) = x
+}
+
+class B : A<String>(), I2<String> {
+    override val prop
+        get() = "3"
+}
+
+fun box(): String {
+    val i: I<String> = B()
+    var result = i.f() + i.g() + i.h()
+    if (result != "123") return "fail1: $result"
+
+    val b = B()
+    result = b.f() + b.g() + b.h()
+    if (result != "123") return "fail2: $result"
+
+    val a: A<String> = B()
+    result = a.f("q") + a.g("w") + a.h("e")
+    if (result != "qwe") return "fail3: $result"
+
+    return "OK"
+}

compiler/testData/codegen/box/defaultArguments/implementedByFake3.kt

@@ -0,0 +1,48 @@
+// IGNORE_BACKEND: JVM, JS
+
+interface I<T> {
+    val prop: T
+
+    fun f(x: String = "1"): String
+
+    fun g(x: String = "2"): String
+
+    fun h(x: T = prop): T
+}
+
+interface I2<T> : I<T> {
+    override fun f(x: String): String
+
+    override fun g(x: String): String
+
+    override fun h(x: T): T
+}
+
+open class A<T> {
+    open fun f(x: String) = x
+
+    open fun g(x: T) = x
+
+    open fun h(x: String) = x
+}
+
+class B : A<String>(), I2<String> {
+    override val prop
+        get() = "3"
+}
+
+fun box(): String {
+    val i: I<String> = B()
+    var result = i.f() + i.g() + i.h()
+    if (result != "123") return "fail1: $result"
+
+    val b = B()
+    result = b.f() + b.g() + b.h()
+    if (result != "123") return "fail2: $result"
+
+    val a: A<String> = B()
+    result = a.f("q") + a.g("w") + a.h("e")
+    if (result != "qwe") return "fail3: $result"
+
+    return "OK"
+}